1. Field of the Invention
The present invention relates to the field of semiconductor wafer processing equipment. More particularly, the present invention relates to a method and apparatus for aligning a wafer on a wafer support member.
2. Background of the Related Art
In the fabrication of integrated circuits, the various processes, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and etch processes, are often carried out in a vacuum environment to, among other things, reduce the particulate level to which the wafers are exposed. Wafers are introduced into a vacuum processing system through a loadlock where robots within the vacuum processing system move the wafers from the loadlock into a transfer chamber and then sequentially through the system positioning the wafers in a series of processing chambers.
The processing steps carried out within the vacuum chambers typically require the deposition, or etching of multiple metal, dielectric and semiconductor film layers on the surface of a wafer. During these processing steps, one must properly align and secure the wafer in the processing chamber in which the desired deposition or etch process is performed.
Typically, the wafer is supported in the chamber on a support member, commonly called a susceptor or pedestal. The wafer is placed on or secured to, the upper surface of the support member prior to the deposition or etch process. To ensure proper processing of the wafer, the wafer must be properly aligned relative to the support member. The position of the support member in the chamber is selected to provide a desired spacing and relative geometry between the generally planar surface of the wafer and other portions of the process chamber such as a gas plate in a CVD process or a target in a PVD process.
Generally, a shadow or clamp ring is used to shield the edge of a wafer and/or, in the case of a clamp ring, secure the wafer to the support member. Although the present invention is equally applicable to both shadow rings and clamp rings, the following description will refer primarily to shadow rings such as those typically used in CVD processes. In addition to acting as a shield, shadow rings also function in wafer capturing or alignment on the support member. Wing members extend downwardly and outwardly from the shadow ring to form a funnel. As the support member moves the wafer upward into the processing position, the support member moves the wafer into the funnel which directs the wafer into alignment with the shadow ring and the support member. Consequently, the funnel applies vertical and lateral forces to the wafer when the slanted wing members achieve lateral alignment of a misaligned wafer with the shadow ring and support member as the support member moves the wafer to the top end of the funnel and the shadow ring settles on the support member.
A primary goal of wafer processing is to obtain as many useful die as possible from each wafer. Many factors influence the processing of wafers in the chamber and effect the ultimate yield of die from each wafer processed therein including the existence of contaminants within the chamber that can attach to the wafer and contaminate one or more die therein. The processing chambers have many sources of particle contaminants which, if received on the wafer, reduce the die yield. One source of particulate contamination occurs when a misaligned wafer is introduced into the chamber. As the wing members of the shadow ring align with the wafer, the wafer slides on the flat surface of the support member and, due to the frictional forces between the wafer and the support member, may create particulate contaminants. In some cases, the frictional forces between the wafer and the support member cause the misaligned wafer to actually move the shadow ring, thereby preventing proper alignment of the wafer and reducing repeatability of the zone of exclusion shielded by the shadow ring and the process.
Prior efforts aimed at reducing the creation of particles have reduced the alignment movement of the wafer on the support member and simply increased the amount of overhang by the shadow ring. In this way, the shadow ring is able to cover the wafer without substantial movement of the wafer. One way that this is accomplished is by increasing the diameter of the shadow ring funnel upper end so that this diameter is larger relative to the diameter of the wafer and the support member. Thus, rather than substantially moving the wafers to align them, these systems simply accept a greater misalignment and accept greater coverage of the wafer upper surface area.
However, a second factor influencing the processing of wafers in the chamber and affecting the ultimate yield of die from each wafer processed therein is the repeatability of the positioning of the wafer and the area covered by the shadow ring. The wafer must be properly aligned relative to the support member and the shadow ring to ensure that the film is properly deposited on the wafer. Therefore, these prior efforts that avoid alignment of the wafer and cover more surface area are not acceptable.
It would, therefore, be desirable to provide a relatively simple system and method for reducing the coefficient of friction between the support member and the wafer that would allow alignment of the wafer without substantial particle generation.
In view of the foregoing, it is an object of the invention to provide a relatively simple apparatus and method for reducing the frictional forces between the support member and the wafer. It is another object of the invention to enhance repeatability and to provide a shadow ring that covers a minimal area of the upper surface of the wafer. Yet another object of the invention is to provide a system and method for aligning a wafer that is relatively inexpensive, efficient, simple to implement, and reliable. Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The present invention provides methods and apparatuses for aligning a wafer on a support member in a vacuum chamber. In one aspect of the invention, the method comprises the steps of introducing the wafer into the vacuum chamber, increasing the pressure within the vacuum chamber and moving the wafer into alignment with a support member and/or shadow ring.
In another aspect, the method comprises providing a shadow ring having a lower portion that is outwardly tapered for receipt of a wafer and an upper aperture having a diameter that is slightly less than the outer diameter of the wafer, introducing the wafer into the vacuum chamber and onto the support member, increasing the pressure within the chamber, and subsequently moving the support member towards the shadow ring so that the shadow ring aligns the wafer on the support member.
In accordance with the methods, the apparatus for aligning a wafer on a support member in a vacuum chamber is an apparatus comprising a support member positioned within the vacuum enclosure and having a wafer receiving surface thereon, a shadow ring located within the vacuum chamber, a gas supply in fluid communication with the vacuum chamber, and a gas flow controller that controls the flow of gas to the vacuum chamber and, thereby, regulates the pressure within the vacuum chamber such that, after the wafer is positioned on the support member and before the wafer is raised into the shadow ring, the gas flow controller raises the pressure within the chamber to about 1 Torr. The shadow ring used in this apparatus comprises an upper shield portion defining a circular aperture therethrough, the circular aperture having a diameter that is slightly less than the outer diameter of the wafer, a lower portion extending from the upper shield portion having an annular cross section defining a frustoconical inner cavity, the diameter of the inner cavity decreases from a lower mouth aperture to an upper end, and the diameter of the upper end of the inner cavity is slightly greater than the outer diameter of the wafer.
In each of these methods and apparatuses, the pressure is preferably raised to a pressure greater than about 1 Torr and more preferably to a pressure between about 1 Torr and 100 Torr and most preferably between about 1 Torr and 10 Torr. Further, the pressure is raised is to approximately equal to or less than the process pressure. Also, the pressure between the wafer and the support member is preferably equal to or greater than the pressure in the chamber before the wafer is aligned.